.obj exportation is not working properly
Nvm I found the answer, it is pretty easy actually. You need to go to the &quot;show overlays&quot; tab (the 3'rd one)

Then press the drop-down and enable &quot;Face Orientation&quot;

After that, all of the faces should blue on the outside and red on the inside.
To inverse them u need to select the wrong ones and go to &quot;Mesh&quot; then &quot;Normals&quot; and &quot;Flip&quot;.
(Or Alt+N and Flip)

Also, u can apply a solidify modifier so that u completely hide the red part.
Easy